The effect of incorporating chalcogenophene comonomers, namely, furan, thiophene, and selenophene, on the optoelectrical properties of cyclopentadithiophene-based polymers (P1, P2, and P3, respectively) for organic field-effect transistors is reported. The optical, electrical, and morphological properties of the P1, P2, and P3 are investigated. Compared to the other polymers, the P2 showed the highest crystallinity with the shortest π–π stacking distance (dπ–π ≈ 3.58 Å) and the longest crystalline length (Lc ≈ 40 Å), as confirmed by two-dimensional grazing incidence wide-angle X-ray diffraction. However, P3 had the highest hole mobility (μ = 0.25 cm2/V-s), which is higher than P1 (μ = 0.06 cm2/V-s) and P2 (μ = 0.20 cm2/V-s). The relatively lower mobility of the P2 compared to that of the P3 is attributed to its island-like crystalline domains, confirmed by atomic force mi-croscopy results and the lower edge-on crystallite ratio. Our findings suggest a new design guideline for developing high-mobility π-conjugated polymers.